Fiber-optic reflectometry techniques are used for detecting and analyzing impairments and events that affect the optical properties of an optical fiber. Various fiber-optic reflectometry techniques are known in the art.
Some fiber-optic reflectometry techniques are based on Optical Frequency-Domain Reflectometry (OFDR). OFDR-based schemes are described, for example, by Zhou et al., in “Distributed vibration sensing with time-resolved optical frequency-domain reflectometry,” Optical Express, volume 20, issue 12, 2012, pages 13138-13145; by Arbel and Eyal, in “Dynamic optical frequency domain reflectometry,” Optics Express, volume 22, issue 8, 2014, pages 8823-8830; and by Bar-Am et al., in “OFDR with double interrogation for dynamic and quasi-distributed sensing,” Optics Express, volume 22, issue 3, 2014, pages 2299-2308, which are incorporated herein by reference.
Additional OFDR schemes are suggested by Eickhoff and Ulrich, in “Optical frequency domain reflectometry in single mode fiber,” Applied Physics Letters, volume 39, issue 9, 1981, pages 693-695; by Soller et al., in “Optical frequency domain reflectometry for single- and multi-mode avionics fiber-optics applications,” IEEE Conference on Avionics, Fiber Optics and Photonics, 2006, pages 38-39; and by Barfuss and Brinkmeyer, in “Modified optical frequency domain reflectometry with high spatial resolution for components of integrated optic systems,” Journal of Lightwave Technology, volume 7, issue 1, 1989, pages 3-10, which are incorporated herein by reference.
Yet additional OFDR techniques are described by Soller et al., in “High resolution optical frequency domain reflectometry for characterization of components and assemblies,” Optics Express, volume 13, issue 2, 2005, pages 666-674; and by Mussi et al., in “−152.5 dB sensitivity high dynamic-range optical frequency domain reflectometry,” Electronics Letters, issue 32, volume 10, 1996, pages 926-927, which are incorporated herein by reference.
Various techniques have been suggested for generating frequency-scanning optical signals used in OFDR. One approach uses an electro-optical modulator that is external to the laser. Such techniques are described, for example, by Tsuji et al., in “Coherent optical frequency domain reflectometry for a long single-mode optical fiber using a coherent lightwave source and an external phase modulator,” IEEE Photonics Technology Letters, volume 7, issue 7, 1995, pages 804-806; by Fan et al., in “Centimeter-level spatial resolution over 40 km realized by bandwidth-division phase-noise-compensated OFDR,” Optics Express, volume 19, 2011, pages 19122-19128; by Fan et al., in “Phase-noise-compensated optical frequency domain reflectometry with measurement range beyond laser coherence length realized using concatenative reference method,” Optics Letters, volume 32, issue 22, 2007, pages 3227-3229; and by Ito et al., in “Long-range coherent OFDR with light source phase noise compensation,” Journal of Lightwave Technology, volume 30, issue 8, 2012, pages 1015-1024, which are incorporated herein by reference.
A different approach for generating frequency-scanning optical signals is to directly modulate one of the laser parameters. Techniques of this sort are suggested, for example, by Passy et al., in “Experimental and theoretical investigations of coherent OFDR with semiconductor laser sources,” Journal of Lightwave Technology, volume 12, issue 9, 1994, pages 1622-1630; by Geng et al., in “Narrow linewidth fiber laser for 100-km optical frequency domain reflectometry,” IEEE Photonics Technology Letters, volume 17, issue 9, 2005, pages 1827-1829; and by Li et al, in “A linearly frequency modulated narrow linewidth single-frequency fiber laser,” Laser Physics Letters, volume 10, issue 7, 2013, which are incorporated herein by reference.